How to emit a single particle using SFML's Thor Particle System

Usecase: shells dropping in sync with firing, fake bullets, etc

You must use a particle emitter to create particles, however this doesn’t mean it’s impossible to create single particles on command. You can create a particle emitter which simply adds particles from a queue to the system

#pragma once
#include <SFML/Graphics.hpp>
#include <Thor/Math.hpp>
#include <Thor/Graphics.hpp>
#include <Thor/Particles.hpp>

namespace sfext {

class SingleParticleEmitter
{
    std::vector<thor::Particle> *particles;
public:
    SingleParticleEmitter();
    SingleParticleEmitter(const SingleParticleEmitter& that);
    void operator() (thor::EmissionInterface& system, sf::Time dt);

    void push(thor::Particle particle);
    void push(sf::Vector2f position, sf::Vector2f velocity, float lifetime, float rot=0, float rotsp=0);
};

}; // end namesapce sfext

The above allows you to use the push functions to emit particles. Here is an example of it in use:

SingleParticleEmitter single_emitter;
thor::ParticleSystem particle_system;
particle_system.addEmitter(single_emitter);

// When you need to emit a shell:

single_emitter.push(origin, velocity, 1.0f);
// lifetime of the particle in seconds --^

Here is the cpp file:

#include "singleparticleemitter.hpp"

using namespace sfext;

SingleParticleEmitter::SingleParticleEmitter()
{
    particles = new std::vector<thor::Particle>();
}

SingleParticleEmitter::SingleParticleEmitter(const SingleParticleEmitter& that)
{
    particles = that.particles;
}

void SingleParticleEmitter::operator() (thor::EmissionInterface& system, sf::Time dt)
{
    for (auto particle : *particles) {
        system.emitParticle(particle);
    }
    particles->clear();
}

void SingleParticleEmitter::push(thor::Particle particle)
{
    particles->push_back(particle);
}

void SingleParticleEmitter::push(sf::Vector2f position, sf::Vector2f velocity, float lifetime, float rot, float rotsp)
{
    thor::Particle particle(sf::seconds(lifetime));
    particle.position = position;
    particle.velocity = velocity;
    particle.rotation = rot;
    particle.rotationSpeed = rotsp;
    particle.scale = sf::Vector2f(1.f, 1.f);
    particle.color = sf::Color::White;
    particle.textureIndex = 0u;
    push(particle);
}